android - 位置在启动时始终为空

Question

当我的应用程序启动时，我试图获取我的纬度和经度，但它总是空的。如果我出去再次打开应用程序，我就会得到位置。

我的代码是：

主要活动

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {  

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.drawer_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
        ViewPager viewPager = findViewById(R.id.view_pager);
        viewPager.setAdapter(sectionsPagerAdapter);
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();
        navigationView.setNavigationItemSelectedListener(this);


        if (ContextCompat.checkSelfPermission(getApplicationContext(),
                android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
                ActivityCompat.checkSelfPermission(getApplicationContext(),
                        android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this,
                    new String[]{
                            android.Manifest.permission.ACCESS_FINE_LOCATION,
                            android.Manifest.permission.ACCESS_COARSE_LOCATION
                    }, 101);
        } else {
            fetchLocation();
        }

    }


    public void fetchLocation() {
        FusedLocationProviderClient mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
        mFusedLocationClient.getLastLocation()
                .addOnSuccessListener(this, new OnSuccessListener<Location>() {
                    @Override
                    public void onSuccess(Location location) {
                        // Got last known location. In some rare situations this can be null.
                        if (location != null) {
                            latlang.Lat = location.getLatitude();
                            latlang.Lang = location.getLongitude();
                            System.out.println("Received Location");
                        }
                    }
                });
    }

latlang在单独的文件中定义为：

public class latlang {
    public static double Lat;
    public static double Lang;
}

负责显示结果的片段是：

public class SunFragment extends Fragment {

    List<SunSession> sunsList;
    Typeface sunfont;


    //to be called by the MainActivity
    public SunFragment() {
        // Required empty public constructor
    }

    // Keys for storing activity state.
//  private static final String KEY_CAMERA_POSITION = "camera_position";
    private static final String KEY_LOCATION_NAME = "location_name";
    public String location;//="No location name found";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Retrieve location and camera position from saved instance state.
        if (savedInstanceState != null) {
            location = savedInstanceState.getCharSequence(KEY_LOCATION_NAME).toString();
            System.out.println("OnCreate location  "+location);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.fragment_sun, container, false);
        onSaveInstanceState(new Bundle());
        //SecondFragment secondFragment = new SecondFragment();
        //secondFragment.getDeviceLocation();

        RecyclerView rv = rootView.findViewById(R.id.rv_recycler_view);
        rv.setNestedScrollingEnabled(false);
        rv.setHasFixedSize(true);
        //MyAdapter adapter = new MyAdapter(new String[]{"Today", "Golden Hour", "Blue Hour", "Civil Twilight", "Nautical Twilight", "Astronomical Twilight", "Hello", "World"});
        //rv.setAdapter(adapter);
        LinearLayoutManager llm = new LinearLayoutManager(getActivity());
        rv.setLayoutManager(llm);
        System.out.println("location  "+location);



   /*
     Reversegeocoding location
     */
        String location="No location name found";
        String errorMessage = "";
        List<Address> addresses = null;

        Geocoder geocoder = new Geocoder(getContext(), Locale.getDefault());
        try {
            addresses = geocoder.getFromLocation(
                    latlang.Lat,
                    latlang.Lang,
                    1);
        } catch (IOException ioException) {
            // Catch network or other I/O problems.
            errorMessage = getString(R.string.service_not_available);
            // Log.e(TAG, errorMessage, ioException);
            if (getView() != null){
                Snackbar.make(getView(), errorMessage, Snackbar.LENGTH_LONG).show();
            }
        } catch (IllegalArgumentException illegalArgumentException) {
            // Catch invalid latitude or longitude values.
            errorMessage = getString(R.string.invalid_lat_long_used);
            if (getView() != null){
                Snackbar.make(getView(),
                        "Illegal Latitude = " + latlang.Lat + ", Longitude = " +
                                latlang.Lang, Snackbar.LENGTH_LONG).show();
            }
        }
        if (addresses == null || addresses.size() == 0) {
            if (errorMessage.isEmpty()) {
                System.out.println("Adress Empty No Address Found");// Snackbar.LENGTH_LONG).show();
                location = "Lat:"+latlang.Lat+" Lang: "+latlang.Lang;
            }
        } else {
            location = addresses.get(0).getAddressLine(0);//+", "+ addresses.get(0).getLocality();
        /* for(int i = 0; i <= addresses.get(0).getMaxAddressLineIndex(); i++) {
          location = addresses.get(0).getAddressLine(i);
        }*/
        }

有人可以帮我把这个位置弄对吗？